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In: Waiting_for_Writeup
ECRIT B. Rosen
Internet-Draft NeuStar, Inc.
Intended status: Standards Track H. Schulzrinne
Expires: February 12, 2016 Columbia U.
H. Tschofenig
August 11, 2015
Data-Only Emergency Calls
draft-ietf-ecrit-data-only-ea-10.txt
Abstract
RFC 6443 'Framework for Emergency Calling Using Internet Multimedia'
describes how devices use the Internet to place emergency calls and
how Public Safety Answering Points (PSAPs) can handle Internet
multimedia emergency calls natively. The exchange of multimedia
traffic typically involves a SIP session establishment starting with
a SIP INVITE that negotiates various parameters for that session.
In some cases, however, the transmission of application data is
everything that is needed. Examples of such environments include a
temperature sensors issuing alerts, or vehicles sending crash data.
Often these alerts are conveyed as one-shot data transmissions.
These type of interactions are called 'data-only emergency calls'.
This document describes a container for the data based on the Common
Alerting Protocol (CAP) and its transmission using the SIP MESSAGE
transaction.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 12, 2016.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
4. Protocol Specification . . . . . . . . . . . . . . . . . . . 6
4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Profiling of the CAP Document Content . . . . . . . . . . 7
4.3. Sending a Data-Only Emergency Call . . . . . . . . . . . 8
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. 425 (Bad Alert Message) Response Code . . . . . . . . . . 9
5.2. The AlertMsg-Error Header Field . . . . . . . . . . . . . 9
6. Updates to the CAP Message . . . . . . . . . . . . . . . . . 11
7. Call Backs . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Handling Large Amounts of Data . . . . . . . . . . . . . . . 11
9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11.1. Registration of the 'application/emergencyCall.cap+xml'
MIME type . . . . . . . . . . . . . . . . . . . . . . . 17
11.2. IANA Registration of Additional Data Block . . . . . . . 18
11.3. IANA Registration for 425 Response Code . . . . . . . . 18
11.4. IANA Registration of New AlertMsg-Error Header Field . . 19
11.5. IANA Registration for the SIP AlertMsg-Error Codes . . . 19
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
13.1. Normative References . . . . . . . . . . . . . . . . . . 20
13.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
RFC 6443 [RFC6443] describes how devices use the Internet to place
emergency calls and how Public Safety Answering Points (PSAPs) can
handle Internet multimedia emergency calls natively. The exchange of
multimedia traffic typically involves a SIP session establishment
starting with a SIP INVITE that negotiates various parameters for
that session.
In some cases, however, there is only application data to be conveyed
from the end devices to a PSAP or some other intermediary. Examples
of such environments includes sensors issuing alerts, or vehicles
sending crash data. These messages may be one-shot alerts to
emergency authorities and do not require establishment of a session.
These type of interactions are called 'data-only emergency calls'.
In this document, we use the term "call" so that similarities between
full sessions with interactive media can be exploited.
Data-only emergency calls are similar to regular emergency calls in
the sense that they require the emergency indications, emergency call
routing functionality and may even have the same location
requirements. However, the communication interaction will not lead
to the exchange of interactive media, that is, Real-Time Protocol
packets, such as voice, video data or real-time text.
The Common Alerting Protocol (CAP) [cap] is a document format for
exchanging emergency alerts and public warnings. CAP is mainly used
for conveying alerts and warnings between authorities and from
authorities to citizen/individuals. This document is concerned with
citizen to authority "alerts", where the alert is sent without any
interactive media.
This document describes a method of including a CAP message in a SIP
transaction, either by value (CAP message is in the body of the
message, using a CID) or by reference (A URI is included in the
message, which when dereferenced returns the CAP message) by defining
it as a block of "additional data" as defined in
[I-D.ietf-ecrit-additional-data]. The additional data mechanism is
also used to send alert specific data beyond that available in the
CAP message. This document also describes how a SIP MESSAGE
[RFC3428] transaction can be used to send a data-only call.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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3. Architectural Overview
This section illustrates two envisioned usage modes; targeted and
location-based emergency alert routing.
1. Emergency alerts containing only data are targeted to a
intermediary recipient responsible for evaluating the next steps.
These steps could include:
1. Sending a call containing only data toward a Public Safety
Answering Point (PSAP);
2. Establishing a third-party initiated emergency call towards a
PSAP that could include audio, video, and data.
2. Emergency alerts may be targeted to a Service URN used for IP-
based emergency calls where the recipient is not known to the
originator. In this scenario, the alert may contain only data
(e.g., a CAP, Geolocation header and one or more Call-Info
headers containing Additional Data
[I-D.ietf-ecrit-additional-data] in a SIP MESSAGE).
Figure 1 shows a deployment variant where a sensor, is pre-configured
(using techniques outside the scope of this document) to issue an
alert to an aggregator that processes these messages and performs
whatever steps are necessary to appropriately react on the alert.
For example, a security firm may use different sensor inputs to
dispatch their security staff to a building they protect or to
initiate a third-party emergency call.
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+------------+ +------------+
| Sensor | | Aggregator |
| | | |
+---+--------+ +------+-----+
| |
Sensors |
trigger |
emergency |
alert |
| MESSAGE with CAP |
|----------------------------->|
| |
| Aggregator
| processes
| emergency
| alert
| 200 (OK) |
|<-----------------------------|
| |
| |
Figure 1: Targeted Emergency Alert Routing
In Figure 2 a scenario is shown whereby the alert is routed using
location information and the Service URN. An emergency services
routing proxy (ESRP) may use LoST to determine the next hop proxy to
route the alert message to. A possible receiver is a PSAP and the
recipient of the alert may be call taker. In the generic case, there
is very likely no prior relationship between the originator and the
receiver, e.g. PSAP. A PSAP, for example, is likely to receive and
accept alerts from entities it cannot authorize. This scenario
corresponds more to the classical emergency services use case and the
description in [RFC6881] is applicable. In this use case, the only
difference between an emergency call, and an emergency data-only call
is that the former uses INVITE, creates a session and negotiates one
or more media streams, while the latter uses MESSAGE, does not create
a session and does not have media.
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+-----------+ +----------+
+--------+ | ESRP | | PSAP |
| Sensor | | | | |
+---+----+ +---+-------+ +---+------+
| | |
Sensors | |
trigger | |
emergency | |
alert | |
| | |
| | |
| MESSAGE with CAP | |
| (including Service URN, |
| such as urn:service:sos) |
|------------------->| |
| | |
| ESRP performs |
| emergency alert |
| routing |
| | MESSAGE with CAP |
| | (including identity info) |
| |----------------------------->|
| | |
| | PSAP
| | processes
| | emergency
| | alert
| | 200 (OK) |
| |<-----------------------------|
| | |
| 200 (OK) | |
|<-------------------| |
| | |
| | |
Figure 2: Location-Based Emergency Alert Routing
4. Protocol Specification
4.1. CAP Transport
A CAP message may be sent on the initial message of any SIP
transaction. However, this document only describes specific behavior
when used with a SIP INVITE that would accompany a normal emergency
call and a SIP MESSAGE transaction for a one-shot, data-only
emergency call. Behavior with other transactions is not defined.
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The CAP message included in a SIP message as an additional-data block
[I-D.ietf-ecrit-additional-data]. Accordingly, it is introduced to
the SIP message with a Call-Info header with a purpose of
"emergencyCall.cap". The header may contain a URI that is used by
the recipient (or in some cases, an intermediary) to obtain the CAP
message. Alternative, the Call-Info header may contain a Content
Indirect url [RFC2392] and the CAP message included in the body of
the message. In either case, the CAP message is located in a MIME
block. The MIME type is set to 'application/emergencyCall.cap+xml'.
If the server does not support the functionality required to fulfill
the request then a 501 Not Implemented MUST be returned as specified
in RFC 3261 [RFC3261]. This is the appropriate response when a UAS
does not recognize the request method and is not capable of
supporting it for any user.
The 415 Unsupported Media Type error MUST be returned as specified in
RFC 3261 [RFC3261] if the server is refusing to service the request
because the message body of the request is in a format not supported
by the server for the requested method. The server MUST return a
list of acceptable formats using the Accept, Accept-Encoding, or
Accept-Language header field, depending on the specific problem with
the content.
4.2. Profiling of the CAP Document Content
The usage of CAP MUST conform to the specification provided with
[cap]. For the usage with SIP the following additional requirements
are imposed:
sender: A few sub-categories for putting a value in the <sender>
element have to be considered:
Originator is a SIP entity, Author indication irrelevant: When
the alert was created by a SIP-based originator and it is not
useful to be explicit about the author of the alert then the
<sender> element MUST be populated with the SIP URI of the user
agent.
Originator is a non-SIP entity, Author indication irrelevant: In
case that the alert was created by a non-SIP based entity and
the identity of this original sender wants to be preserved then
this identity MUST be placed into the <sender> element. In
this category the it is not useful to be explicit about the
author of the alert. The specific type of identity being used
will depends on the technology being used by the original
originator.
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Author indication relevant: In case the author is different from
the actual originator of the message and this distinction
should be preserved then the <sender> element MUST NOT contain
the SIP URI of the user agent.
incidents: The <incidents> element MUST be present. This incident
identifier MUST be chosen in such a way that it is unique for a
given <sender, expires, incidents> combination. Note that the
<expires> element is optional and may not be present.
scope: The value of the <scope> element MAY be set to "Private" if
the alert is not meant for public consumption. The <addresses>
element is, however, not used by this specification since the
message routing is performed by SIP and the respective address
information is already available in other SIP headers. Populating
information twice into different parts of the message may lead to
inconsistency.
parameter: The <parameter> element MAY contain additional
information specific to the sendor.
area: It is RECOMMENDED to omit this element when constructing a
message. In case that the CAP message already contained an <area>
element then the specified location information SHOULD be copied
into the PIDF-LO structure of the 'geolocation' header.
4.3. Sending a Data-Only Emergency Call
A data-only emergency call is sent using a SIP MESSAGE transaction
with a CAP URI or body as described above in a manner similar to how
an emergency call with interactive media is sent, as described in
[RFC6881]. The MESSAGE transaction does not create a session or send
media, but otherwise, the header content of the transaction, routing,
and processing of data-only calls are the same as those of other
emergency calls.
5. Error Handling
This section defines a new error response code and a header field for
additional information.
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5.1. 425 (Bad Alert Message) Response Code
This SIP extension creates a new location-specific response code,
defined as follows,
425 (Bad Alert Message)
The 425 response code is a rejection of the request due to its
included alert content, indicating that it was malformed or not
satisfactory for the recipient's purpose.
A SIP intermediary can also reject an alert it receives from a UA
when it understands that the provided alert is malformed.
Section 5.2 describes an AlertMsg-Error header field with more
details about what was wrong with the alert message in the request.
This header field MUST be included in the 425 response.
It is only appropriate to generate a 425 response when the responding
entity has no other information in the request that are usable by the
responder.
A 425 response code MUST NOT be sent in response to a request that
lacks an alert message entirely, as the user agent in that case may
not support this extension at all.
A 425 response is a final response within a transaction, and MUST NOT
terminate an existing dialog.
5.2. The AlertMsg-Error Header Field
The AlertMsg-Error header provides additional information about what
was wrong with the original request. In some cases the provided
information will be used for debugging purposes.
The AlertMsg-Error header field has the following ABNF [RFC5234]:
message-header /= AlertMsg-Error
; (message-header from 3261)
AlertMsg-Error = "AlertMsg-Error" HCOLON
ErrorValue
ErrorValue = error-code
*(SEMI error-params)
error-code = 1*3DIGIT
error-params = error-code-text
/ generic-param ; from RFC3261
error-code-text = "code" EQUAL quoted-string ; from RFC3261
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HCOLON, SEMI, and EQUAL are defined in RFC3261 [RFC3261]. DIGIT is
defined in RFC5234 [RFC5234].
The AlertMsg-Error header field MUST contain only one ErrorValue to
indicate what was wrong with the alert payload the recipient
determined was bad.
The ErrorValue contains a 3-digit error code indicating what was
wrong with the alert in the request. This error code has a
corresponding quoted error text string that is human understandable.
The text string are OPTIONAL, but RECOMMENDED for human readability,
similar to the string phrase used for SIP response codes. That said,
the strings are complete enough for rendering to the user, if so
desired. The strings in this document are recommendations, and are
not standardized - meaning an operator can change the strings - but
MUST NOT change the meaning of the error code. Similar to how RFC
3261 specifies, there MUST NOT be more than one string per error
code.
The AlertMsg-Error header field MAY be included in any response as an
alert message was in the request part of the same transaction. For
example, a UA includes an alert in an MESSAGE to a PSAP. The PSAP
can accept this MESSAGE, thus creating a dialog, even though his UA
determined the alert message contained in the MESSAGE was bad. The
PSAP merely includes an AlertMsg-Error header value in the 200 OK to
the MESSAGE informing the UA that the MESSAGE was accepted but the
alert provided was bad.
If, on the other hand, the PSAP cannot accept the transaction without
a suitable alert message, a 425 response is sent.
A SIP intermediary that requires the UA's alert message in order to
properly process the transaction may also sends a 425 with a
AlertMsg-Error code.
This document defines an initial list of error code ranges for any
SIP response, including provisional responses (other than 100 Trying)
and the new 425 response. There MUST be no more than one AlertMsg-
Error code in a SIP response.
AlertMsg-Error: 100 ; code="Cannot Process the Alert Payload"
AlertMsg-Error: 101 ; code="Alert Payload was not present or could
not be found"
AlertMsg-Error: 102 ; code="Not enough information to determine the
purpose of the alert"
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AlertMsg-Error: 103 ; code="Alert Payload was corrupted"
Additionally, if an entity cannot or chooses not to process the alert
message from a SIP request, a 500 (Server Internal Error) SHOULD be
used with or without a configurable Retry-After header field.
6. Updates to the CAP Message
If the sender anticipates that the content of the CAP message may
need to be updated during the lifecycle of the event referred to in
the message, it may include an update block as defined in
[I-D.rosen-ecrit-addldata-subnot].
7. Call Backs
This document does not describe any method for the recipient to call
back the sender of the data-only call. Usually, these alerts are
sent by automata, and do not have any mechanism to receive calls of
any kind. The identifier in the From header may be useful to obtain
more information, but any such mechanism is not defined in this
document. The CAP message may contain related contact information
for the sender.
8. Handling Large Amounts of Data
It is not atypical for sensor to have large quantities of data that
they may wish to send. Including large amounts of data in a MESSAGE
is not advisable, because SIP entities are usually not equipped to
handle very large messages. In such cases, the sender SHOULD make
use of the by-reference mechanisms defined for Additional Data which
involve sending a URI in the Call-Info header and using HTTPS to
retrieve the data. The CAP message itself can be sent by-reference
using this mechanism as well as any or all of the Additional Data
blocks that may contain sensor-specific data.
9. Example
Figure 3 shows a CAP document indicating a BURGLARY alert issued by a
sensor called 'sensor1@domain.com'. The location of the sensor can
be obtained from the attached location information provided via the
'geolocation' header contained in the SIP MESSAGE structure.
Additionally, the sensor provided some data long with the alert
message using proprietary information elements only to be processed
by the receiver, a SIP entity acting as an aggregator. This example
reflects the description in Figure 1.
MESSAGE sip:aggregator@domain.com SIP/2.0
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Via: SIP/2.0/TCP sensor1.domain.com;branch=z9hG4bK776sgdkse
Max-Forwards: 70
From: sip:sensor1@domain.com;tag=49583
To: sip:aggregator@domain.com
Call-ID: asd88asd77a@1.2.3.4
Geolocation: <cid:abcdef@domain.com>
;routing-allowed=yes
Supported: geolocation
Accept: application/pidf+xml, application/emergencyCall.cap+xml
CSeq: 1 MESSAGE
Call-Info: cid:abcdef2@domain.com;purpose=emergencyCall.cap
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/emergencyCall.cap
Content-ID: <abcdef2@domain.com>
Content-Disposition: by-reference;handling=optional
<?xml version="1.0" encoding="UTF-8"?>
<alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
<identifier>S-1</identifier>
<sender>sip:sensor1@domain.com</sender>
<sent>2008-11-19T14:57:00-07:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Private</scope>
<incidents>abc1234</incidents>
<info>
<category>Security</category>
<event>BURGLARY</event>
<urgency>Expected</urgency>
<certainty>Likely</certainty>
<severity>Moderate</severity>
<senderName>SENSOR 1</senderName>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE1</valueName>
<value>123</value>
</parameter>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE2</valueName>
<value>TRUE</value>
</parameter>
</info>
</alert>
--boundary1
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Content-Type: application/pidf+xml
Content-ID: <abcdef2@domain.com>
Content-Disposition: by-reference;handling=optional
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp=
"urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="sensor">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--
Figure 3: Example Message conveying an Alert to an Aggregator
Figure 4 shows the same CAP document sent as a data-only emergency
call towards a PSAP.
MESSAGE urn:service:sos SIP/2.0
Via: SIP/2.0/TCP sip:aggreg.1.example.com;branch=z9hG4bK776abssa
Max-Forwards: 70
From: sip:aggregator@example.com;tag=32336
To: 112
Call-ID: asdf33443a@example.com
Route: sip:psap1.example.gov
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Geolocation: <cid:abcdef@example.com>
;routing-allowed=yes
Supported: geolocation
Accept: application/pidf+xml, application/emergencyCall.cap+xml
Call-info: cid:abcdef2@domain.com;purpose=emergencyCall.cap
CSeq: 1 MESSAGE
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/emergencyCall.cap+xml
Content-ID: <abcdef2@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
<identifier>S-1</identifier>
<sender>sip:sensor1@domain.com</sender>
<sent>2008-11-19T14:57:00-07:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Private</scope>
<incidents>abc1234</incidents>
<info>
<category>Security</category>
<event>BURGLARY</event>
<urgency>Expected</urgency>
<certainty>Likely</certainty>
<severity>Moderate</severity>
<senderName>SENSOR 1</senderName>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE1</valueName>
<value>123</value>
</parameter>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE2</valueName>
<value>TRUE</value>
</parameter>
</info>
</alert>
--boundary1
Content-Type: application/pidf+xml
Content-ID: <abcdef2@domain.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
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xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp=
"urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="sensor">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--
Figure 4: Example Message conveying an Alert to a PSAP
10. Security Considerations
This section discusses security considerations when SIP user agents
issue emergency alerts utilizing MESSAGE and CAP. Location specific
threats are not unique to this document and are discussed in
[RFC7378] and [RFC6442].
The ECRIT emergency services architecture [RFC6443] considers
classical individual-to-authority emergency calling and the identity
of the emergency caller does not play a role at the time of the call
establishment itself, i.e., a response to the emergency call will not
depend on the identity of the caller. In case of emergency alerts
generated by devices, like sensors, the processing may be different
in order to reduce the number of falsely generated emergency alerts.
Alerts may get triggered based on certain sensor input that may have
been caused by other factors than the actual occurrence of an alert
relevant event. For example, a sensor may simply be malfunctioning.
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For this purpose not all alert messages are directly sent to a PSAP
but rather may be pre-processed by a separate entity, potentially
under supervision by a human, to filter alerts and potentially
correlate received alerts with others to obtain a larger picture of
the ongoing situation.
In any case, for alerts that are initiated by sensors the identity
may play an important role in deciding whether to accept or ignore an
incoming alert message. With the scenario shown in Figure 1 it is
very likely that only authorized sensor input will be processed. For
this purpose it needs to be ensured that no alert messages from an
unknown origin are accepted. Two types of information elements can
be used for this purpose:
1. SIP itself provides security mechanisms that allow the
verification of the originator's identity. These mechanisms can
be re-used, such as P-Asserted-Identity [RFC3325] or SIP Identity
[RFC4474]. The latter provides a cryptographic assurance while
the former relies on a chain of trust model.
2. CAP provides additional security mechanisms and the ability to
carry additional information about the sender's identity.
Section 3.3.2.1 of [cap] specifies the signing algorithms of CAP
documents.
In addition to the desire to perform identity-based access control
the classical communication security threats need to be considered,
including integrity protection to prevent forgery and replay of alert
messages in transit. To deal with replay of alerts a CAP document
contains the mandatory <identifier>, <sender>, <sent> elements and an
optional <expire> element. These attributes make the CAP document
unique for a specific sender and provide time restrictions. An
entity that has received a CAP message already within the indicated
timeframe is able to detect a replayed message and, if the content of
that message is unchanged, then no additional security vulnerability
is created. Additionally, it is RECOMMENDED to make use of SIP
security mechanisms, such as SIP Identity [RFC4474], to tie the CAP
message to the SIP message. To provide protection of the entire SIP
message exchange between neighboring SIP entities the usage of TLS is
mandatory.
Note that none of the security mechanism in this document protect
against a compromised sensor sending crafted alerts.
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11. IANA Considerations
11.1. Registration of the 'application/emergencyCall.cap+xml' MIME type
To: ietf-types@iana.org
Subject: Registration of MIME media type application/
emergencyCall.cap+xml
MIME media type name: application
MIME subtype name: cap+xml
Required parameters: (none)
Optional parameters: charset; Indicates the character encoding of
enclosed XML. Default is UTF-8 [RFC3629].
Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See RFC
3023 [RFC3023], Section 3.2.
Security considerations: This content type is designed to carry
payloads of the Common Alerting Protocol (CAP).
Interoperability considerations: This content type provides a way to
convey CAP payloads.
Published specification: RFC XXX [Replace by the RFC number of this
specification].
Applications which use this media type: Applications that convey
alerts and warnings according to the CAP standard.
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Additional information: OASIS has published the Common Alerting
Protocol at http://www.oasis-open.org/committees/
documents.php&wg_abbrev=emergency
Person and email address to contact for further information: Hannes
Tschofenig, Hannes.Tschofenig@nsn.com
Intended usage: Limited use
Author/Change controller: IETF ECRIT working group
Other information: This media type is a specialization of
application/xml RFC 3023 [RFC3023], and many of the considerations
described there also apply to application/cap+xml.
11.2. IANA Registration of Additional Data Block
This document registers a new block type in the sub-registry called
'Additional Data Blocks' defined in [I-D.ietf-ecrit-additional-data].
The token is "cap" and the reference is this document.
11.3. IANA Registration for 425 Response Code
In the SIP Response Codes registry, the following is added
Reference: RFC-XXXX (i.e., this document)
Response code: 425 (recommended number to assign)
Default reason phrase: Bad Alert Message
Registry:
Response Code Reference
------------------------------------------ ---------
Request Failure 4xx
425 Bad Alert Message [this doc]
This SIP Response code is defined in Section 5.
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11.4. IANA Registration of New AlertMsg-Error Header Field
The SIP AlertMsg-error header field is created by this document, with
its definition and rules in Section 5, to be added to the IANA sip-
parameters registry with two actions:
1. Update the Header Fields registry with
Registry:
Header Name compact Reference
----------------- ------- ---------
AlertMsg-Error [this doc]
2. In the portion titled "Header Field Parameters and Parameter
Values", add
Predefined
Header Field Parameter Name Values Reference
----------------- ------------------- ---------- ---------
AlertMsg-Error code yes [this doc]
11.5. IANA Registration for the SIP AlertMsg-Error Codes
This document creates a new registry for SIP, called "AlertMsg-Error
Codes". AlertMsg-Error codes provide reason for the error discovered
by recipients, categorized by action to be taken by error recipient.
The initial values for this registry are shown below.
Registry Name: AlertMsg-Error Codes
Reference: [this doc]
Registration Procedures: Specification Required
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Code Default Reason Phrase Reference
---- --------------------------------------------------- ---------
100 "Cannot Process the Alert Payload" [this doc]
101 "Alert Payload was not present or could not be found" [this doc]
102 "Not enough information to determine
the purpose of the alert" [this doc]
103 "Alert Payload was corrupted" [this doc]
Details of these error codes are in Section 5.
12. Acknowledgments
The authors would like to thank the participants of the Early Warning
adhoc meeting at IETF#69 for their feedback. Additionally, we would
like to thank the members of the NENA Long Term Direction Working
Group for their feedback.
Additionally, we would like to thank Martin Thomson, James
Winterbottom, Shida Schubert, Bernard Aboba, and Marc Linsner for
their review comments.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[cap] Jones, E. and A. Botterell, "Common Alerting Protocol v.
1.1", October 2005.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
<http://www.rfc-editor.org/info/rfc2392>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
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[RFC3428] Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
Huitema, C., and D. Gurle, "Session Initiation Protocol
(SIP) Extension for Instant Messaging", RFC 3428, DOI
10.17487/RFC3428, December 2002,
<http://www.rfc-editor.org/info/rfc3428>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, DOI 10.17487/RFC3023, January 2001,
<http://www.rfc-editor.org/info/rfc3023>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC6442] Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
for the Session Initiation Protocol", RFC 6442, DOI
10.17487/RFC6442, December 2011,
<http://www.rfc-editor.org/info/rfc6442>.
[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013,
<http://www.rfc-editor.org/info/rfc6881>.
[I-D.ietf-ecrit-additional-data]
Gellens, R., Rosen, B., Tschofenig, H., Marshall, R., and
J. Winterbottom, "Additional Data Related to an Emergency
Call", draft-ietf-ecrit-additional-data-33 (work in
progress), July 2015.
[I-D.rosen-ecrit-addldata-subnot]
Rosen, B., "Updating Additional Data related to an
Emergency Call using Subscribe/ Notify", draft-rosen-
ecrit-addldata-subnot-01 (work in progress), November
2013.
13.2. Informative References
[RFC7378] Tschofenig, H., Schulzrinne, H., and B. Aboba, Ed.,
"Trustworthy Location", RFC 7378, DOI 10.17487/RFC7378,
December 2014, <http://www.rfc-editor.org/info/rfc7378>.
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[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, DOI 10.17487/
RFC4474, August 2006,
<http://www.rfc-editor.org/info/rfc4474>.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325, DOI
10.17487/RFC3325, November 2002,
<http://www.rfc-editor.org/info/rfc3325>.
[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling Using Internet
Multimedia", RFC 6443, DOI 10.17487/RFC6443, December
2011, <http://www.rfc-editor.org/info/rfc6443>.
Authors' Addresses
Brian Rosen
NeuStar, Inc.
470 Conrad Dr
Mars, PA 16046
US
Email: br@brianrosen.net
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Hannes Tschofenig
Hall in Tirol 6060
Austria
Email: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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